Nachi Ket Mehta

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3G Wireless Systems Nachiket Mehta Wireless Networks CSG250 OUTLINE 3G Overview Advantage, Capabilities, Organizations, IMT-2000 radio interface, Technologies, Evolution paths UMTS-FDD / WCDMA Spreading Codes, Physical layer, Mac layer, RLC layer, RRC layer Hand Over Power Control QoS Support Whats next after 3G? Summary References 3G Overview Route to 3G 1G: analog 2G : 1st digital mobile telephony 2.5G: transition from 2G to 3G 3G standard: IMT 2000 3G & Future Wireless Vs. Bandwidth 1001,00010,000100,0001,000,00010,000,000100,000,0001,000,000,00010,000,000,0001960 1970 1980 1990 2000 2010bps GPRS 3G 4G 2G 3.5G 3G- Advantages 3G phones promise :- Improved digital voice communications Larger Bandwidth Higher Data rate Greater subscriber capacity Fast packet-based data services like e-mail, short message service (SMS), and Internet access at broadband speeds. Most carriers also expect consumers to want :- location services interactive gaming streaming video home monitoring and control and who knows what else, while being fully mobile anywhere in the world.3G Capabilities Voice quality comparable to the public switched telephone network 144 Kbps- user in high-speed motor vehicles 384 Kbps- pedestrians standing or moving slowly over small areas Up to 2 Mbps- fixed applications like office use Symmetrical/asymmetrical data transmission rates Support for both packet switched and circuit switched data services like Internet Protocol (IP) traffic and real time video Organizations 3G is also known as UMTS (Universal Mobile Telecommunication System) 3GPP 3rd Generation Partnership Project. 3GPP2 3rd Generation Partnership Project 2 Internet Engineering Taskforce (IETF) ITU-IMT-2000 Standard (International Telecommunication Union- International Mobile Telecommunication) IMT-DS UMTS-FDD (WCDMA) Direct spread IMT-MC CDMA-2000 (1x-EvDO/DV) Multi carrier IMT-TC UMTS-TDD (TD-SCDMA) Time code IMT-SC UWC-136 (EDGE) Single carrier IMT-FT DECT Freq. time CDMA TDMAFDMA IMT-2000 Radio Interface I M T Paired Spectrum Unpaired Spectrum IMT-2000 Frequency Bands 1G + 2G 806 960 MHz 2G (Asia, Europe) + 3G 1710 1885 MHz DECT, PHS + 2G + 3G 1885202521102200 MHz 25002690 MHz WCDMA(UL)1820-1880MHz WCDMA(DL)1910-1970MHz Technologies 3G is superior to the other digital standards like:- GSM (Global System for Mobile) communications standard used worldwide And IS-136 TDMA standard used primarily in North America. 3G Technologies:- WCDMA or UMTS-FDD (Universal Mobile Telecommunications System - Frequency Division Duplex)---Direct Spread CDMA2000 - 1x-EvDO/EvDV---Multi carrier UMTS TDD (Time Division Duplex) or TD-SCDMA (Time Division - Synchronous Code Division Multiple Access) ---Time Code 4G Technologies:- Digital Audio Broadcast (DAB) and Digital Video Broadcast (DVB) for wide area broadcasting Local Multipoint Distribution System (LMDS) Microwave Multipoint Distribution System (MMDS) Wireless Technologies (Figure) Evolution Paths 2.5G2G 3G cdmaOne IS-95A TDMA cdmaOne IS-95B Cdma2000 1X Cdma2000 1xEV-DV Cdma2000 1xEV-DO GSM GPRS EDGE WCDMA GSM Map Core Network IS-41 Core Network UMTS-FDD / WCDMA (Universal Mobile Telecommunication Standard- Frequency Division Duplex) UMTS-FDD / WCDMA Wideband Direct Sequence Code Division Multiple Access Does not assign a specific frequency to each user. Instead every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence Narrowband option for TDD. WCDMA Parameters Channel B.W5 MHz Forward RF Channel StructureDirect Spread Chip Rate3.84 Mcps Frame Length10 ms (38400 chips) No. of slots/frame15 No. of chips/slot2560chips (Max. 2560 bits) Power ControlOpen and fast close loop (1.6 KHz) Uplink SF4 to 256 Downlink SF4 to 512 Spreading Operation Spreading means increasing the signal bandwidth Strictly speaking, spreading includes two operations: (1) Channelisation (increases signal bandwidth) - using orthogonal codes (2) Scrambling (does not affect the signal bandwidth) - using pseudo noise codes Codes Channellization CodeScrambling Code UsageUL: Separation of physical data and control channels from same UE DL: Separation of different users within one cell UL: Separation of terminals DL: Separation of cells/sectors LengthUL:4-256 chips DL:4-512 chips 38400 chips No. of codes No. of codes under one scrambling code= SF UL: Several million DL: 512 Code Family Orthogonal Variable Spreading FactorLong 10ms code: Gold code Short code: Extended S(2) code Family Increase B.W? YESNO UMTS/IMT-2000 Architecture UMTS Protocol Stack WCDMA : PHYSICAL Layer Physical Layer The physical layer offers information transfer services to the MAC layer. These services are denoted as Transport channels (TrChs). There are also Physical channels. Physical layer comprises following functions: Various handover functions Error detection and report to higher layers Multiplexing of transport channels Mapping of transport channels to physical channels Fast Close loop Power control Frequency and Time Synchronization Other responsibilities associated with transmitting and receiving signals over the wireless media. Transport & Physical Channels Transport ChannelPhysical Channel (UL/DL) Dedicated Channel DCHDedicated Physical Data Channel DPDCH Dedicated Physical Control Channel DPCCH (UL) Random Access Channel RACHPhysical random access channel PRACH (UL) Common packet channel CPCHPhysical common packet channel PCPCH (DL) Broadcast channel BCHPrimary common control physical channel P-CCPCH (DL) Forward access channel FACH (DL) Paging channel PCH Secondary common control physical channel S-CCPCH (DL) Downlink shared channel DSCHPhysical downlink shared channel PDSCH Signaling physical channels Synchronization channel SCH Common pilot channel CPICH Acquisition indication channel AICH Paging indication channel PICH CPCH Status indication channel CSICH Collision detection/Channel assignment indicator channel CD/CA-ICH WCDMA : MAC Layer MAC Layer The MAC layer offers Data transfer to RLC and higher layers. The MAC layer comprises the following functions: Selection of appropriate TF (basically bit rate), within a predefined set, per information unit delivered to the physical layer Service multiplexing on RACH, FACH, and dedicated channels Priority handling between data flows of one user as well as between data flows from several usersthe latter being achieved by means of dynamic scheduling Access control on RACH Address control on RACH and FACH Contention resolution on RACH WCDMA : RLC Layer RLC Layer The RLC layer offers the following services to the higher layers: Layer 2 connection establishment/release Transparent data transfer, i.e., no protocol overhead is appended to the information unit received from the higher layer Assured and un assured data transfer The RLC layer comprises the following functions: Segmentation and assembly Transfer of user data Error correction by means of retransmission optimized for the WCDMA physical layer Sequence integrity (used by at least the control plane) Duplicate detection Flow control Ciphering WCDMA : RRC Layer RRC Layer The RRC layer offers the core network the following services: General control service, which is used as an information broadcast service Notification service, which is used for paging and notification of a selected UEs Dedicated control service, which is used for establishment/release of a connection and transfer of messages using the connection. The RRC layer comprises the following functions: Broadcastinginformation from network to all UEs Radio resource handling (e.g., code allocation, handover,admission control, and measurement reporting/control) QoS Control UE measurement reporting and control of the reporting Power Control, Encryption and Integrity protection WCDMA : Hand Over Hand Over Intra-mode handover Include soft handover, softer handover and hard handover. Rely on the Ec/No measurement performed from the CPICH. Inter-mode handover Handover to the UTRA TDD mode. Inter-system handover Handover to other system, such as GSM. Make measurement on the frequency during compressed mode. WCDMA : Power Control Power Control Fast Closed Loop PC Inner Loop PC Feedback information. Uplink PC is used for near-far problem. Downlink PC is to ensure that there is enough power for mobiles at the cell edge. Two special cases for fast closed loop PC: Soft handover:- how to react to multiple power control commands from several sources. At the mobile, a power down command has higher priority over power up command. Compressed mode:- Large step size is used after a compressed frame to allow the power level to converge more quickly to the correct value after the break. Power Control (Contd.) Open loop PC No feedback information. Make a rough estimate of the path loss by means of a downlink beacon signal. Provide a coarse initial power setting of the mobile at the beginning of a connection. Apply only prior to initiating the transmission on RACH or CPCH. WCDMA : QoS Support UMTS/WCDMA QoS The standard provides an overview of the functionality needed to establish, modify and maintain a UMTS link with a specific QoS. Divided into: Control plane Managing, translating, admitting and controlling users requests and network resources. User plane QoS signaling and monitoring of user data traffic QoS Classes Conversational (real time):- VoIP Telephony Video conferencing Streaming (real time):- Video and audio streams Interactive:- Web browsing Data retrieval Server access Background:- Download of emails and files What next after 3G? 199020002010 GSM (2G) W-CDMA (3G) GPRS/ EDGE (2.5G) The future path has fractured into a number of possibilities Operators and vendors must create viable strategies to prosper within this complexity 4G 3G+ 3G & WLAN 3G & WLAN & Brdcst 3G+ & WLAN 3G & WLA